Multifunctional broadband electromagnetic wave-absorbing composite material based on bionic periodic unit and multistage core-shell filler and preparation method thereof

Abstract

The invention discloses a multifunctional broadband electromagnetic wave-absorbing composite material based on a bionic periodic unit and a multistage core-shell filler and a preparation method thereof.The multistage core-shell filler is used as a raw material, an impregnation technology is adopted, and the bionic periodic unit is impregnated by preparing high-loss paint and impedance matching paint with different concentrations; the electromagnetic wave-absorbing composite material is obtained. Accurate gradient distribution and better impedance matching of electromagnetic parameters in a three-dimensional space are achieved, the density is lower than 6 kg / m under the thickness of 15-20 mm, the plane compression strength is 2 MPa, and the effective absorption bandwidth (RLlt;-10 dB) covers 8-18 GHz. The invention solves the contradiction between the bandwidth, thickness, weight and single function of the traditional wave-absorbing material, and is suitable for the fields of advanced stealth equipment and electromagnetic protection. The material opens up a new direction for the development of electromagnetic wave-absorbing materials, and is expected to be widely applied to many fields such as national defense, communication, electronics and the like.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic wave absorbing composite material technology, and particularly relates to a multifunctional broadband electromagnetic wave absorbing composite material based on biomimetic periodic units and multi-level core-shell fillers and its preparation method. Background Technology

[0002] With the rapid development of modern electronic information technology, fifth-generation mobile communication technology, radar detection, electronic countermeasures, and other technological fields have made rapid progress. In the application of these technologies, the rational control and utilization of electromagnetic waves has become crucial. The 8-18GHz (X / Ku band) is a core frequency band for radar guidance, satellite communication, and other systems, making the demand for high-efficiency absorbing materials for this band extremely urgent.

[0003] Based on different electromagnetic wave loss mechanisms, absorbing materials can be classified into dielectric loss type and magnetic loss type. Existing absorbing materials mainly rely on ferrites, conductive carbon materials (such as carbon nanotubes, graphene), or simple physical mixtures thereof as absorbers, and are prepared using coating or lamination processes. However, these traditional methods have many inherent drawbacks that are difficult to overcome: At the material level, the density is relatively high, which is not conducive to meeting the requirements of lightweight absorbing materials; the electromagnetic wave attenuation capability mainly comes from the magnetic loss mechanism, the dielectric loss is insufficient, and the impedance matching is poor; most of them are solid structures with high density and low electromagnetic wave loss efficiency.

[0004] From a structural perspective, achieving good impedance gradient matching is difficult, and interlayer interface reflection is significant. To broaden the bandwidth, it is often necessary to increase the material thickness, which sharply contradicts the current trend of lightweight and thin equipment development, severely restricting the application of absorbing materials in some fields with stringent requirements for weight and thickness.

[0005] At the functional level, traditional microwave absorbing materials are single-function, focusing only on absorption performance while lacking integrated functions such as thermal management and structural load-bearing. With the development of intelligent and multifunctional modern advanced equipment, such single-function materials can no longer meet the demand for multifunctional composite materials.

[0006] The issues at the fabrication level cannot be ignored. Traditional mixing, coating, and molding processes cannot achieve precise control over the composition and structure of materials in three-dimensional space, making it difficult to fabricate complex curved conformal structures. Furthermore, these processes suffer from problems such as filler settling and weak interfacial bonding, severely impacting the performance and lifespan of microwave absorbing materials.

[0007] Therefore, there is a need for a microwave absorbing material that combines wide bandwidth and thinness, with improvements in material structure design and manufacturing process.

[0008] Patent application CN120573706A discloses a Fe3C@C assembled nanostructure and its preparation method. The surface array of C nanoparticles and the hollow structure of this nanostructure significantly enhance the multiple scattering effect of electromagnetic waves. The numerous Fe3C-C heterostructure interfaces promote the enhancement of interfacial polarization relaxation loss, thus improving absorption performance. However, the Fe3C@C structure is a hollow sphere with a thickness of 2.4 mm, resulting in weak impact resistance and making it unsuitable for use as a load-bearing structural component. Furthermore, this method does not solve the technical problem of achieving optimal impedance gradient matching. Summary of the Invention

[0009] To address the aforementioned technical problems, this invention provides a multifunctional broadband electromagnetic wave absorbing composite material based on biomimetic periodic units and multi-level core-shell fillers, and its preparation method.

[0010] The present invention is achieved through the following technical solutions.

[0011] The present invention provides a multifunctional broadband electromagnetic wave absorbing composite material based on biomimetic periodic units and multi-level core-shell fillers, comprising biomimetic periodic units, wherein the biomimetic periodic units are hexagonal honeycomb structures.

[0012] A method for preparing a multifunctional broadband electromagnetic absorbing composite material based on biomimetic periodic units and multi-level core-shell fillers includes the following steps: A1: Carbon nanotube arrays were grown in situ on the surface of a magnetic core by chemical vapor deposition, and metal oxide nanoparticles were grafted onto the ends of the carbon nanotubes to obtain a multi-level core-shell filler. A2: High-loss coatings and impedance matching coatings were prepared using multi-level core-shell fillers as one of the raw materials. A3: Using impregnation technology, by configuring high-loss coatings and impedance matching coatings of different concentrations, the prepared biomimetic periodic units are impregnated to obtain electromagnetic wave absorbing composite materials.

[0013] Preferably, the method for preparing multi-stage core-shell packing includes the following steps: B1: The substrate material is placed as a magnetic core into a fluidized bed reactor and charged with 300~600 sccm of carrier gas, 100~300 sccm of reducing gas and 100~200 sccm of carbon source gas; B2: Increase the temperature from room temperature to 100-200℃ at a rate of 2-8℃ / min and hold for 1-3 hours to obtain CIP@VACNTs with carbon nanotubes generated on the magnetic core; B3: Metal oxide nanoparticles are grafted onto the ends of carbon nanotubes using a solvothermal method; B4: Wash with deionized water and ethanol alternately 2-5 times, and vacuum dry at 40-70℃ for 10-15h to obtain CIP@VACNTs@Fe3O4 multi-level core-shell packing.

[0014] Preferably, the substrate material is spherical carbonyl iron powder, the carrier gas is argon, the reducing gas is hydrogen, and the carbon source gas is ethylene.

[0015] Preferably, the metal oxide nanoparticles in step B3 are Fe3O4 nanoparticles, and the grafting step includes: adding CIP@VACNTs to an ethylene glycol solution to obtain a mixture, then adding FeCl3・6H2O and sodium acetate to the mixture, ultrasonically dispersing for 15~45 min; then transferring to a reaction vessel, reacting at a constant temperature of 150~200℃ for 8~15 h, and naturally cooling to room temperature.

[0016] Preferably, the preparation of the high-loss coating includes the following steps: C1: Place the multi-stage core-shell filler, thermally conductive flexible polymer, diluent, and thixotropic agent into a mixer and stir at 1200~1700 rpm for 15~40 min to obtain mixture A; C2: Grind the mixture 2 to 5 times until the final viscosity of mixture A is 1×10⁵ cP to 1.5×10⁵ cP; The preparation of the impedance matching coating includes the following steps: D1: Place the multi-stage core-shell packing material, spherical material, thermally conductive flexible polymer, diluent and thixotropic agent into a mixer and stir at 1200~1700 rpm for 15~40 min to obtain mixture B; D2: Grind the mixture 2 to 5 times until the final viscosity of mixture B is 7×10⁴ cP to 10×10⁴ cP.

[0017] Preferably, the spherical material is glass microspheres with a particle size of 10~20μm, the thermally conductive flexible polymer includes thermally conductive silicone rubber or polyurethane, the diluent is xylene, and the thixotropic agent is fumed silica.

[0018] Preferably, in step A3, the biomimetic periodic unit is impregnated with a high-loss coating as the innermost layer and an impedance matching coating as the outermost layer, and the impregnation is performed sequentially.

[0019] Preferably, the impregnation process of the electromagnetic absorbing composite material includes: E1: Preprocessing The biomimetic periodic units were rinsed with deionized water. After cleaning, the bionic cycle unit is placed in a drying equipment for pre-drying; E2: Immersion Operation The pretreated biomimetic periodic unit is placed in the immersion tank; Slowly add the prepared high-loss coating as impregnation liquid into the impregnation tank. The amount of impregnation liquid added should be enough to submerge 2 / 3 of the biomimetic cycle unit. The biomimetic periodic unit is immersed in the impregnation solution for 30-60 minutes; E3: Post-processing After soaking, the biomimetic periodic unit is removed from the immersion tank and excess immersion liquid is removed from the surface by draining. The drained biomimetic cycle units are placed in a drying device for drying. E4: After drying, the bionic periodic unit is cooled to room temperature. Then, according to the parameters in step E3, the remaining 1 / 3 of the other side of the bionic periodic unit is impregnated with impedance matching coating to obtain electromagnetic wave absorbing composite material.

[0020] Preferably, the impregnation process of the electromagnetic absorbing composite material includes: E1: Preprocessing The biomimetic periodic units were rinsed with deionized water for 5-10 minutes at a pressure of 0.2-0.3 MPa. After cleaning, the bionic cycle unit is placed in a drying equipment for pre-drying at a temperature of 60-80℃ for 1-2 hours. E2: Immersion Operation The pretreated biomimetic periodic unit is placed in the immersion tank; Slowly add the prepared high-loss coating as impregnation liquid into the impregnation tank. The amount of impregnation liquid added should be enough to submerge 2 / 3 of the biomimetic cycle unit. Start the vacuum equipment and evacuate the impregnation tank. The vacuum level is controlled between -0.085MPa and -0.095MPa, and the evacuation time is 15~30min. After vacuuming is completed, turn off the vacuum equipment and keep the biomimetic cycle unit immersed in the impregnation solution for 30-60 minutes. During the immersion process, stir the impregnation solution at a speed of 50-100 r / min to ensure uniform concentration of the impregnation solution. E3: Post-processing After soaking, the biomimetic periodic unit is removed from the immersion tank and the excess immersion liquid on the surface is removed by draining. The draining time is 5 to 10 minutes. After draining, the biomimetic cycle units are placed in a drying equipment for drying at a temperature of 80~120℃ for 2~4 hours. E4: After drying, the bionic periodic unit is cooled to room temperature. Then, according to the parameters in step E3, the remaining 1 / 3 of the other side of the bionic periodic unit is impregnated with impedance matching coating to obtain electromagnetic wave absorbing composite material.

[0021] The beneficial effects of this invention are as follows: 1. The multi-level core-shell filler prepared in this invention achieves strong coupling and multi-frequency resonance of magnetic / dielectric loss at the nanoscale; the biomimetic periodic structure achieves excellent impedance gradient and multiple scattering of electromagnetic waves. This synergistic effect enables an effective absorption bandwidth of <-10dB covering an extremely wide frequency band of 8-18GHz with an average value of -15.61dB and a minimum absorption point below -22.97dB, even with a thickness of 15-20mm. This means that the material can achieve efficient electromagnetic wave absorption over an extremely wide frequency band, meeting the broadband absorption requirements of different fields and devices.

[0022] 2. The biomimetic periodic unit utilizes a hexagonal honeycomb porous structure to reduce the areal density to below 6 kg / m² while maintaining performance. It also boasts a planar compressive strength of 2 MPa and excellent specific strength and impact resistance, making it suitable for use as a load-bearing structural component. This lightweight and high-strength characteristic gives the material broad application prospects in aerospace, electronic equipment, and other fields with high requirements for weight and strength.

[0023] 3. The thermally conductive flexible polymer matrix used in this invention, together with VACNTs, forms a highly efficient thermal conduction path, enabling rapid dissipation of heat generated by electromagnetic waves and preventing thermal failure. In practical applications, the absorption of electromagnetic waves by the absorbing material generates heat. If heat cannot be dissipated in time, it will affect the material's performance and service life. The thermal management function effectively solves this technical problem. This function allows the electromagnetic wave absorbing composite structure to provide real-time feedback on its status, providing important information for equipment maintenance and fault diagnosis, and improving the reliability and safety of the equipment. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the electromagnetic wave absorbing composite material of the present invention; Figure 2 This is a schematic diagram of the structure of the multi-stage core-shell packing material of the present invention; Figure 3 This is a schematic diagram of the biomimetic periodic unit impregnation of the present invention; Figure 4 This is a reflectance curve diagram of Embodiment 3 of the present invention; In the figure: 1-Bionic periodic unit, 101-Inner layer, 102-Outer layer, 2-Magnetic core, 3-Carbon nanotube, 4-Metal oxide nanoparticle. Detailed Implementation

[0025] The technical solution of the present invention is further described below, but the scope of protection is not limited to what is described.

[0026] The electromagnetic wave absorbing composite material based on multi-level core-shell filler in this application belongs to magnetic wave absorbing materials.

[0027] When electromagnetic waves are incident on the surface of an absorbing material, two main processes occur: 1. Impedance matching: Minimize interface reflections to allow electromagnetic waves to enter the material.

[0028] 2. Loss mechanism: The energy of the incoming electromagnetic wave is irreversibly converted into heat energy.

[0029] For magnetic absorbing materials, their internal microstructure can be equivalent to a circuit model under the action of an electromagnetic field.

[0030] When electromagnetic waves are incident on a magnetic absorbing material, both an electric field-driven conductive current and a magnetic field-driven magnetization process are simultaneously generated. These two processes together form the internal circuit of the magnetic absorbing material, converting electromagnetic energy into heat energy through different loss mechanisms, thereby achieving wave absorption. The role of current in magnetic absorbing materials is manifested in directly converting electromagnetic energy into heat energy.

[0031] In the preparation method of electromagnetic absorbing composite structure based on multi-level core-shell packing: Magnetic core: Composed of spherical carbonyl iron powder (CIP) or iron-silicon-aluminum powder, it mainly provides the magnetic loss mechanism and is the key part of the microwave absorbing material to achieve magnetic loss.

[0032] The dielectric intermediate shell consists of vertically oriented carbon nanotube arrays (VACNTs) grown in situ on the surface of the magnetic core using chemical vapor deposition (CVD). It not only provides dielectric loss but also enhances interfacial polarization, further improving the material's microwave absorption performance.

[0033] Magnetic nano-modified outer layer: composed of iron(III) oxide (Fe3O4) or other magnetic metal nanoparticles modified at the ends of carbon nanotubes by grafting, used to adjust high-frequency resonance characteristics and further enhance loss, so that the material has good wave absorption effect in a wider frequency band.

[0034] High-loss coatings: A high-viscosity, high-filler-content composite coating is prepared by mixing a pre-mixed multi-stage core-shell filler with a thermally conductive flexible polymer prepolymer, diluent, and thixotropic agent, followed by high-speed shear dispersion and three-roll milling. The purpose of high-speed shear dispersion and three-roll milling is to ensure uniform dispersion of the filler in the coating and avoid agglomeration.

[0035] Impedance matching coatings: This involves reducing the content of core-shell fillers in high-loss coatings or adding microspheres with low dielectric constants, such as glass microspheres, to create a coating system with a gradual change in dielectric constant. By adjusting the filler content or adding microspheres, the electromagnetic properties of the coating can be precisely controlled to meet the impedance matching requirements of different components.

[0036] Impregnation process steps and parameter control for electromagnetic wave absorbing composite materials: E1: Preprocessing Place the 300mm×300mm×18mm biomimetic periodic unit into the cleaning equipment and rinse it with deionized water for 5~10 minutes. The rinsing pressure is controlled at 0.2~0.3MPa.

[0037] After cleaning, the biomimetic cycle unit is placed in a drying equipment for pre-drying at a temperature of 60-80℃ for 1-2 hours to remove moisture from the material surface and avoid affecting the concentration of the impregnation solution.

[0038] E2: Immersion Operation The pre-treated biomimetic periodic units are neatly placed in the impregnation tank, ensuring that there are certain gaps between the materials to facilitate the flow of the impregnation liquid.

[0039] The prepared high-loss coating is slowly added to the impregnation tank as an impregnation solution. The amount of impregnation solution added is based on immersing 2 / 3 of the biomimetic cycle unit.

[0040] Start the vacuum equipment and evacuate the impregnation tank. Control the vacuum level between -0.085 MPa and -0.095 MPa for 15 to 30 minutes. During the vacuuming process, closely observe the state of the impregnation liquid to prevent it from boiling due to excessive vacuum.

[0041] After vacuuming is completed, the vacuum equipment is turned off, and the biomimetic periodic unit is kept immersed in the impregnation solution. The immersion time is determined according to the concentration of the impregnation solution and the porosity of the biomimetic periodic unit, generally 30-60 minutes. During the immersion process, the impregnation solution is stirred at a speed of 50-100 r / min to ensure uniform concentration.

[0042] E3: Post-processing After soaking, the biomimetic cycle unit is removed from the immersion tank and drained to remove excess immersion liquid from the surface. The draining time is 5-10 minutes to avoid excessive immersion liquid being carried into the drying process, which would cause paint waste and uneven drying.

[0043] After draining, the biomimetic cycle units are placed in a drying device for drying at a temperature of 80-120℃ for 2-4 hours. During the drying process, the drying status of the materials is checked regularly to avoid over-drying or under-drying.

[0044] After drying, the biomimetic periodic units are cooled to room temperature and then subjected to quality testing.

[0045] Following the impregnation process steps and parameter control in step E3, the remaining 1 / 3 of the other side of the biomimetic periodic unit is then impregnated with impedance matching coating to obtain an electromagnetic wave absorbing composite material.

[0046] Example 1: like Figures 1 to 3 As shown, a multifunctional broadband electromagnetic wave absorbing composite material based on biomimetic periodic units and multi-level core-shell fillers includes a biomimetic periodic unit 1 as a skeleton, wherein the biomimetic periodic unit 1 has a hexagonal honeycomb porous structure. The biomimetic periodic unit 1 is made of aramid fiber, and its hexagonal honeycomb structure can effectively disperse external forces, resulting in a robust structure and a high strength-to-weight ratio.

[0047] A method for preparing a multifunctional broadband electromagnetic absorbing composite material based on biomimetic periodic units and multi-level core-shell fillers includes the following steps: A1: Carbon nanotube array 3 was grown in situ on the surface of magnetic core 2 by chemical vapor deposition, and metal oxide nanoparticles 4 were grafted onto the ends of carbon nanotube 3 to obtain multi-level core-shell filler. A2: High-loss coatings and impedance matching coatings were prepared using multi-level core-shell fillers as one of the raw materials. A3: Using impregnation technology, the prepared biomimetic periodic unit 1 is impregnated with high-loss coatings and impedance matching coatings of different concentrations to obtain electromagnetic wave absorbing composite materials.

[0048] The method for preparing multi-stage core-shell packing includes the following steps: B1: Place the substrate material as the magnetic core 2 into the fluidized bed reactor (inner diameter 50mm, height 300mm, quartz material), and fill it with 300sccm of carrier gas, 100sccm of reducing gas and 100sccm of carbon source gas. B2: CIP@VACNTs with carbon nanotubes 3 formed on the magnetic core 2 were obtained by heating from room temperature to 100℃ at a rate of 2℃ / min and holding for 1 h. The carbon nanotube 3 growth results were: vertical orientation >90%, average length 3.2±0.3μm, tube diameter 20~30nm, and array density 1.5×10⁻⁶. 9 roots / cm²; B3: Metal oxide nanoparticles 4 are grafted onto the ends of carbon nanotubes 3 by a solvothermal method; B4: Wash twice with deionized water and ethanol alternately, and vacuum dry at 40℃ for 10h to obtain CIP@VACNTs@Fe3O4 multi-level core-shell packing.

[0049] The substrate material is spherical carbonyl iron powder with a particle size of 5±0.5μm and a specific surface area of ​​1.2m² / g; the carrier gas is argon, the reducing gas is hydrogen, and the carbon source gas is ethylene.

[0050] In step B3, the metal oxide nanoparticles 4 are Fe3O4 nanoparticles. The grafting step includes: adding 10g of CIP@VACNTs to 500ml of ethylene glycol solution to obtain a mixture, then adding 5g of FeCl3・6H2O and 10g of sodium acetate to the mixture, and ultrasonically dispersing for 15min; then transferring to a reaction vessel, reacting at 150℃ for 8h, and naturally cooling to room temperature.

[0051] Fe3O4 nanoparticle modification results: The Fe3O4 nanoparticles have a particle size of 15±3nm and are uniformly distributed at the ends of carbon nanotubes 3.

[0052] The high-loss coating is the inner layer 101, which serves as the core absorbing region, while the impedance matching coating is the outer layer 102.

[0053] The preparation of the high-loss coating includes the following steps: C1: 60wt% multi-stage core-shell filler, 35wt% thermally conductive flexible polymer, 3wt% diluent, and 2wt% thixotropic agent are placed in a planetary mixer and stirred at 1200rpm for 15min to obtain mixture A; C2: The mixture is milled twice in a three-roll mill with a roller gap of 0.05 mm. A rotational viscometer test is performed at 25°C until the final viscosity of mixture A reaches 1×10⁻⁶. 5 cP; The performance parameters of the high-loss coating are: dielectric constant ε'=28 (10GHz) and magnetic permeability μ'=1.8 (10GHz), which meet the electromagnetic parameter requirements of the high-loss region.

[0054] The preparation of the impedance matching coating includes the following steps: D1: 20wt% multi-stage core-shell filler, 10wt% spherical material, 65wt% thermally conductive flexible polymer, 3wt% diluent and 2wt% thixotropic agent are placed in a planetary mixer and stirred at 1200rpm for 15min to obtain mixture B; D2: Grind the mixture twice in a three-roll mill and test the viscosity using a rotational viscometer at 25°C until the final viscosity of mixture B is 7 × 10⁻⁶. 4 cP.

[0055] The dielectric constant ε'=12 (10GHz) of the impedance matching coating enables a gradient transition of dielectric constant from the outer layer 102 to the inner layer 101 (12 to 28).

[0056] The spherical material is a glass microsphere with a particle size of 10~20μm and a dielectric constant ε=3.2. The thermally conductive flexible polymer is polyurethane. As a matrix, the thermally conductive flexible polymer not only has good flexibility and can adapt to complex usage environments, but also has high thermal conductivity, laying the foundation for the thermal management function of the material.

[0057] The diluent is xylene, and the thixotropic agent is fumed silica.

[0058] In step A3, when impregnating the biomimetic periodic unit 1, a high-loss coating is used as the inner layer 101 and an impedance matching coating is used as the outer layer 102.

[0059] Impregnation method for electromagnetic absorbing composite materials: E1: Preprocessing The 300mm×300mm×18mm biomimetic periodic unit 1 was placed in the cleaning equipment and rinsed with deionized water for 10 minutes. The rinsing pressure was controlled at 0.2~0.3MPa.

[0060] After cleaning, the bionic cycle unit 1 is placed in a drying equipment for pre-drying. The pre-drying temperature is maintained at 60~80℃ for 1 hour to remove moisture from the material surface and avoid affecting the concentration of the impregnation solution.

[0061] E2: Immersion Operation The pretreated biomimetic periodic unit 1 is neatly placed into the impregnation tank, ensuring that there are certain gaps between the materials to facilitate the flow of the impregnation liquid.

[0062] The prepared high-loss coating is slowly added to the impregnation tank as the impregnation liquid. The amount of impregnation liquid added is based on immersing 2 / 3 of the bionic periodic unit 1, that is, the bionic periodic unit 1 is immersed to a height of 12mm.

[0063] Start the vacuum equipment and evacuate the impregnation tank, controlling the vacuum level between -0.085 MPa and -0.095 MPa for 15 minutes. During the vacuuming process, closely observe the state of the impregnation liquid to prevent it from boiling due to excessive vacuum.

[0064] After vacuuming is completed, the vacuum equipment is turned off, and the biomimetic periodic unit 1 is kept immersed in the impregnation solution for 30 minutes. During the immersion process, the impregnation solution is stirred at a speed of 80 r / min to ensure uniform concentration.

[0065] E3: Post-processing After soaking, the biomimetic cycle unit 1 is removed from the soaking tank and the excess soaking liquid on the surface is removed by draining. The draining time is 8 minutes to avoid too much soaking liquid being carried into the drying process, which would cause waste of active components and uneven drying.

[0066] After draining, the biomimetic cycle unit 1 is placed in a drying device for drying. The drying temperature is maintained at 80~120℃ for 3 hours. During the drying process, the drying status of the material is checked regularly to avoid over-drying or under-drying.

[0067] Following the impregnation process steps and parameter control in step E3, the remaining 1 / 3 of the other side of the biomimetic periodic unit 1 is then impregnated with impedance matching coating to obtain an electromagnetic wave absorbing composite material.

[0068] Example 2: like Figures 1 to 3 As shown, a multifunctional broadband electromagnetic wave absorbing composite material based on biomimetic periodic units and multi-level core-shell fillers includes a biomimetic periodic unit 1 as a skeleton, wherein the biomimetic periodic unit 1 has a hexagonal honeycomb porous structure. The biomimetic periodic unit 1 is made of aramid fiber, and its hexagonal honeycomb structure can effectively disperse external forces, resulting in a robust structure and a high strength-to-weight ratio.

[0069] A multifunctional broadband electromagnetic absorbing composite material based on biomimetic periodic units and multi-level core-shell fillers and its preparation method, comprising the following steps: A1: Carbon nanotube array 3 was grown in situ on the surface of magnetic core 2 by chemical vapor deposition, and metal oxide nanoparticles 4 were grafted onto the ends of carbon nanotube 3 to obtain multi-level core-shell filler. A2: High-loss coatings and impedance matching coatings were prepared using multi-level core-shell fillers as one of the raw materials. A3: Using impregnation technology, the prepared biomimetic periodic unit 1 is impregnated with high-loss coatings and impedance matching coatings of different concentrations to obtain electromagnetic wave absorbing composite materials.

[0070] The method for preparing multi-stage core-shell packing includes the following steps: B1: Place the substrate material as the magnetic core 2 into the fluidized bed reactor (inner diameter 50mm, height 300mm, quartz material), and fill it with 600 sccm of carrier gas, 300 sccm of reducing gas and 200 sccm of carbon source gas. B2: CIP@VACNTs with carbon nanotubes 3 formed on the magnetic core 2 were obtained by heating from room temperature to 200℃ at a rate of 8℃ / min and holding for 3 hours. The carbon nanotube 3 growth results were: vertical orientation >90%, average length 3.2±0.3μm, tube diameter 20~30nm, and array density 1.5×10⁻⁶. 9 roots / cm²; B3: Metal oxide nanoparticles 4 are grafted onto the ends of carbon nanotubes 3 by a solvothermal method; B4: Washed 5 times alternately with deionized water and ethanol, and vacuum dried at 70℃ for 15h to obtain CIP@VACNTs@Fe3O4 multi-level core-shell packing.

[0071] The substrate material is spherical carbonyl iron powder with a particle size of 5±0.5μm and a specific surface area of ​​1.2m² / g; the carrier gas is argon, the reducing gas is hydrogen, and the carbon source gas is ethylene.

[0072] In step B3, the metal oxide nanoparticles 4 are Fe3O4 nanoparticles. The grafting step includes: adding 10g of CIP@VACNTs to 500ml of ethylene glycol solution to obtain a mixture, then adding 5g of FeCl3・6H2O and 10g of sodium acetate to the mixture, and ultrasonically dispersing for 45min; then transferring to a reaction vessel, reacting at 200℃ for 15h, and naturally cooling to room temperature.

[0073] Fe3O4 nanoparticle modification results: The Fe3O4 nanoparticles have a particle size of 15±3nm and are uniformly distributed at the ends of carbon nanotubes 3.

[0074] The high-loss coating is the inner layer 101, which serves as the core absorbing region, while the impedance matching coating is the outer layer 102, which serves as the surface gradient region.

[0075] The preparation of the high-loss coating includes the following steps: C1: 60wt% multi-stage core-shell filler, 35wt% thermally conductive flexible polymer, 3wt% diluent, and 2wt% thixotropic agent are placed in a planetary mixer and stirred at 1700rpm for 40min to obtain mixture A; C2: The mixture was milled 5 times in a three-roll mill with a roller gap of 0.05 mm, and the viscosity was tested using a rotational viscometer at 25°C until the final viscosity of mixture A was 1.5 × 10⁻⁶. 5 cP; The performance parameters of the high-loss coating are: dielectric constant ε'=28 (10GHz) and magnetic permeability μ'=1.8 (10GHz), which meet the electromagnetic parameter requirements of the high-loss region.

[0076] The preparation of the impedance matching coating includes the following steps: D1: 20wt% multi-stage core-shell filler, 10wt% spherical material, 65wt% thermally conductive flexible polymer, 3wt% diluent and 2wt% thixotropic agent are placed in a planetary mixer and stirred at 1700rpm for 40min to obtain mixture B; D2: The mixture is milled 5 times in a three-roll mill and tested with a rotational viscometer at 25°C until the final viscosity of mixture B is 10 × 10⁻⁶. 4 cP.

[0077] The dielectric constant ε'=12 (10GHz) of the impedance matching coating enables a gradient transition of dielectric constant from the outer layer 102 to the inner layer 101 (12 to 28).

[0078] The spherical material is a glass microsphere with a particle size of 10~20μm and a dielectric constant ε=3.2. The thermally conductive flexible polymer is a thermally conductive silicone rubber. The thermally conductive flexible polymer, as a matrix, not only has good flexibility and can adapt to complex usage environments, but also has high thermal conductivity, laying the foundation for the thermal management function of the material.

[0079] The diluent is xylene, and the thixotropic agent is fumed silica.

[0080] During the impregnation process in step A3, a high-loss coating is used as the innermost layer 101, and an impedance matching coating is used as the outermost layer 102.

[0081] Impregnation steps for electromagnetic absorbing composite materials: E1: Preprocessing The 300mm×300mm×18mm biomimetic periodic unit 1 was placed in the cleaning equipment and rinsed with deionized water for 5 minutes. The rinsing pressure was controlled at 0.2~0.3MPa.

[0082] After cleaning, the bionic cycle unit 1 is placed in a drying equipment for pre-drying. The pre-drying temperature is controlled at 60~80℃ for 2 hours to remove moisture from the surface of the material and avoid affecting the concentration of the impregnation solution.

[0083] E2: Immersion Operation The pretreated biomimetic periodic unit 1 is neatly placed into the impregnation tank, ensuring that there are certain gaps between the materials to facilitate the flow of the impregnation liquid.

[0084] The prepared high-loss coating is slowly added to the impregnation tank as the impregnation liquid. The amount of impregnation liquid added is based on immersing 2 / 3 of the bionic periodic unit 1, that is, the bionic periodic unit 1 is immersed to a height of 12mm.

[0085] Start the vacuum equipment and evacuate the impregnation tank, controlling the vacuum level between -0.085 MPa and -0.095 MPa for 15 minutes. During the vacuuming process, closely observe the state of the impregnation liquid to prevent it from boiling due to excessive vacuum.

[0086] After vacuuming is completed, the vacuum equipment is turned off, and the biomimetic periodic unit 1 is kept immersed in the impregnation solution for 60 minutes. During the immersion process, the impregnation solution is stirred at a speed of 50 r / min to ensure uniform concentration.

[0087] E3: Post-processing After soaking, the biomimetic cycle unit 1 is removed from the soaking tank and the excess soaking liquid on the surface is removed by draining. The draining time is 7 minutes to avoid too much soaking liquid being carried into the drying process, which would cause waste of soaking liquid and uneven drying.

[0088] After draining, the biomimetic cycle unit 1 is placed in a drying device for drying. The drying temperature is maintained at 80~120℃ for 2 hours. During the drying process, the drying status of the material is checked regularly to avoid over-drying or under-drying.

[0089] After drying, the biomimetic periodic unit 1 is cooled to room temperature and then subjected to quality testing.

[0090] Following the impregnation process steps and parameter control in step E3, the remaining 1 / 3 of the other side of the biomimetic periodic unit 1 is then impregnated with impedance matching coating to obtain an electromagnetic wave absorbing composite material.

[0091] Example 3: like Figures 1 to 3 As shown, a multifunctional broadband electromagnetic wave absorbing composite material based on biomimetic periodic units and multi-level core-shell fillers includes a biomimetic periodic unit 1 as a skeleton, wherein the biomimetic periodic unit 1 has a hexagonal honeycomb porous structure. The biomimetic periodic unit 1 is made of aramid fiber, and its hexagonal honeycomb structure can effectively disperse external forces, resulting in a robust structure and a high strength-to-weight ratio.

[0092] A method for preparing a multifunctional broadband electromagnetic absorbing composite material based on biomimetic periodic units and multi-level core-shell fillers includes the following steps: A1: Carbon nanotube array 3 was grown in situ on the surface of magnetic core 2 by chemical vapor deposition, and metal oxide nanoparticles 4 were grafted onto the ends of carbon nanotube 3 to obtain multi-level core-shell filler. A2: High-loss coatings and impedance matching coatings were prepared using multi-level core-shell fillers as one of the raw materials. A3: Using impregnation technology, the prepared biomimetic periodic unit 1 is impregnated with high-loss coatings and impedance matching coatings of different concentrations to obtain electromagnetic wave absorbing composite materials.

[0093] The method for preparing multi-stage core-shell packing includes the following steps: B1: Place the substrate material as the magnetic core 2 into the fluidized bed reactor (inner diameter 50mm, height 300mm, quartz material), and fill it with 500 sccm of carrier gas, 200 sccm of reducing gas and 150 sccm of carbon source gas. B2: CIP@VACNTs with carbon nanotubes 3 formed on the magnetic core 2 were obtained by heating from room temperature to 150℃ at a rate of 5℃ / min and holding for 2 hours. The growth results of carbon nanotubes 3 were: vertical orientation > 90%, average length 3.2 ± 0.3 μm, tube diameter 20~30 nm, and array density 1.5 × 10⁻⁶. 9 roots / cm²; B3: Metal oxide nanoparticles 4 are grafted onto the ends of carbon nanotubes 3 by a solvothermal method; B4: Washed three times alternately with deionized water and ethanol, and then vacuum dried at 60°C for 12 hours to obtain CIP@VACNTs@Fe3O4 multi-level core-shell packing material.

[0094] The substrate material is spherical carbonyl iron powder with a particle size of 5±0.5μm and a specific surface area of ​​1.2m² / g; the carrier gas is argon, the reducing gas is hydrogen, and the carbon source gas is ethylene.

[0095] In step B3, the metal oxide nanoparticles 4 are Fe3O4 nanoparticles. The grafting step includes: adding 10g of CIP@VACNTs to 500ml of ethylene glycol solution to obtain a mixture, then adding 5g of FeCl3・6H2O and 10g of sodium acetate to the mixture, and ultrasonically dispersing for 30min; then transferring to a reaction vessel, reacting at a constant temperature of 180℃ for 12h, and naturally cooling to room temperature.

[0096] Fe3O4 nanoparticle modification results: The Fe3O4 nanoparticles have a particle size of 15±3nm and are uniformly distributed at the ends of carbon nanotubes 3.

[0097] The high-loss coating is the inner layer 101, which serves as the core absorbing region, while the impedance matching coating is the outer layer 102, which serves as the outer gradient region.

[0098] The preparation of the high-loss coating includes the following steps: C1: 60wt% multi-stage core-shell filler, 35wt% thermally conductive flexible polymer, 3wt% diluent, and 2wt% thixotropic agent are placed in a planetary mixer and stirred at 1500rpm for 20min to obtain mixture A; C2: The mixture was milled three times in a three-roll mill with a roller gap of 0.05 mm. The mixture was then tested using a rotational viscometer at 25°C until the final viscosity of mixture A reached 1.2 × 10⁻⁶. 5 cP; The performance parameters of the high-loss coating are: dielectric constant ε'=28 (10GHz) and magnetic permeability μ'=1.8 (10GHz), which meet the electromagnetic parameter requirements of the high-loss region.

[0099] The preparation of the impedance matching coating includes the following steps: D1: 20wt% multi-stage core-shell filler, 10wt% spherical material, 65wt% thermally conductive flexible polymer, 3wt% diluent and 2wt% thixotropic agent are placed in a planetary mixer and stirred at 1500rpm for 20min to obtain mixture B; D2: The mixture is milled three times in a three-roll mill and tested with a rotational viscometer at 25°C until the final viscosity of mixture B is 8 × 10⁻⁶. 4 cP.

[0100] The dielectric constant ε'=12 (10GHz) of the impedance matching coating enables a gradient transition of dielectric constant from the outer layer 102 to the inner layer 101 (12 to 28).

[0101] The spherical material is a glass microsphere with a particle size of 10~20μm and a dielectric constant ε=3.2. The thermally conductive flexible polymer is polyurethane. As a matrix, the thermally conductive flexible polymer not only has good flexibility and can adapt to complex usage environments, but also has high thermal conductivity, laying the foundation for the thermal management function of the material.

[0102] The diluent is xylene, and the thixotropic agent is fumed silica.

[0103] During the impregnation process in step A3, a high-loss coating is used as the inner layer 101, and an impedance matching coating is used as the outer layer 102.

[0104] Impregnation steps for electromagnetic absorbing composite materials: E1: Preprocessing The 300mm×300mm×18mm biomimetic periodic unit 1 was placed in the cleaning equipment and rinsed with deionized water for 5 minutes. The rinsing pressure was controlled at 0.2~0.3MPa.

[0105] After cleaning, the bionic cycle unit 1 is placed in a drying equipment for pre-drying. The pre-drying temperature is maintained at 60~80℃ for 2 hours to remove moisture from the material surface and avoid affecting the concentration of the impregnation solution.

[0106] E2: Immersion Operation The pretreated biomimetic periodic unit 1 is neatly placed into the impregnation tank, ensuring that there are certain gaps between the materials to facilitate the flow of the impregnation liquid.

[0107] The prepared high-loss coating is slowly added to the impregnation tank as the impregnation liquid. The amount of impregnation liquid added is based on immersing 2 / 3 of the bionic periodic unit 1, that is, the bionic periodic unit 1 is immersed to a height of 12mm.

[0108] Start the vacuum equipment and evacuate the impregnation tank, controlling the vacuum level between -0.085 MPa and -0.095 MPa for 20 minutes. During the vacuuming process, closely observe the state of the impregnation liquid to prevent it from boiling due to excessively high vacuum.

[0109] After vacuuming is completed, the vacuum equipment is turned off, and the biomimetic periodic unit 1 is kept immersed in the impregnation solution for 50 minutes. During the immersion process, the impregnation solution is stirred at a speed of 100 r / min to ensure uniform concentration.

[0110] E3: Post-processing After soaking, the biomimetic cycle unit 1 is removed from the soaking tank and the excess soaking liquid on the surface is removed by draining. The draining time is 10 minutes to avoid too much soaking liquid being carried into the drying process, which would cause waste of soaking liquid and uneven drying.

[0111] After draining, the biomimetic cycle unit 1 is placed in a drying device for drying. The drying temperature is maintained at 80~120℃ for 4 hours. During the drying process, the drying status of the material is checked regularly to avoid over-drying or under-drying.

[0112] After drying, the biomimetic periodic unit 1 is cooled to room temperature and then subjected to quality testing.

[0113] Following the impregnation process steps and parameter control in step E3, the remaining 1 / 3 of the other side of the biomimetic periodic unit 1 is then impregnated with impedance matching coating to obtain an electromagnetic wave absorbing composite material.

[0114] The performance of the electromagnetic absorbing composite structure prepared in Example 3 was tested: 1. Electromagnetic absorption performance was tested using the bow-shaped method: Test equipment: Vector network analyzer (P5028A), frequency range 8~18GHz, incident angle 0°.

[0115] Results: With a thickness of 18mm, the effective absorption bandwidth with a reflectivity of <-10dB can cover an extremely wide frequency band of 8~18GHz, with an average value of -15.61dB, and the lowest absorption point can reach below -22.97dB.

[0116] 2. Thermal management performance test: Test method: Laser flare method was used (test equipment model LFA457). In-plane thermal conductivity was 2.52 W / (m·K), vertical thermal conductivity was 1.8 W / (m·K), and thermal diffusivity was 1.2 × 10⁻⁶. -6 m 2 / s, can rapidly dissipate heat while absorbing electromagnetic waves (temperature rise <5℃ / 100mW / cm²). 2Power density).

[0117] 3. Mechanical and lightweight performance testing: Compressive strength: 2 MPa (ASTM D695 standard, loading rate 1 mm / min), specific strength 8.4 × 10³ N·m / kg.

[0118] Surface density: 5.5 kg / m², porosity 72%, meeting the lightweight requirements of the aerospace field.

Claims

1. A multifunctional broadband electromagnetic wave absorbing composite material based on biomimetic periodic units and multi-level core-shell fillers, characterized in that: It includes a biomimetic periodic unit (1), which is a hexagonal honeycomb structure.

2. A method for preparing a multifunctional broadband electromagnetic absorbing composite material based on biomimetic periodic units and multi-level core-shell fillers as described in claim 1, characterized in that: Includes the following steps: A1: Carbon nanotube (3) arrays were grown in situ on the surface of the magnetic core (2) by chemical vapor deposition, and metal oxide nanoparticles (4) were grafted onto the ends of the carbon nanotubes (3) to obtain a multi-level core-shell filler. A2: High-loss coatings and impedance matching coatings were prepared using multi-level core-shell fillers as one of the raw materials. A3: Using impregnation technology, by configuring high-loss coatings and impedance matching coatings of different concentrations, the prepared biomimetic periodic unit (1) is impregnated to obtain electromagnetic wave absorbing composite material.

3. The method for preparing a multifunctional broadband electromagnetic absorbing composite material based on biomimetic periodic units and multi-level core-shell fillers as described in claim 2, characterized in that: The method for preparing multi-stage core-shell packing includes the following steps: B1: The substrate material is placed as a magnetic core (2) into a fluidized bed reactor and filled with 300~600 sccm of carrier gas, 100~300 sccm of reducing gas and 100~200 sccm of carbon source gas; B2: Increase the temperature from room temperature to 100-200℃ at a rate of 2-8℃ / min and hold for 1-3 hours to obtain CIP@VACNTs with carbon nanotubes (3) generated on the magnetic core (2); B3: Metal oxide nanoparticles (4) are grafted onto the ends of carbon nanotubes (3) by a solvothermal method. B4: Wash with deionized water and ethanol alternately 2-5 times, and vacuum dry at 40-70℃ for 10-15h to obtain CIP@VACNTs@Fe3O4 multi-level core-shell packing.

4. The method for preparing a multifunctional broadband electromagnetic absorbing composite material based on biomimetic periodic units and multi-level core-shell fillers as described in claim 3, characterized in that: The substrate material is spherical carbonyl iron powder, the carrier gas is argon, the reducing gas is hydrogen, and the carbon source gas is ethylene.

5. The method for preparing a multifunctional broadband electromagnetic absorbing composite material based on biomimetic periodic units and multi-level core-shell fillers as described in claim 3, characterized in that: The metal oxide nanoparticles (4) in step B3 are Fe3O4 nanoparticles. The grafting step includes: adding CIP@VACNTs to an ethylene glycol solution to obtain a mixture, then adding FeCl3・6H2O and sodium acetate to the mixture, ultrasonically dispersing for 15~45min; then transferring to a reaction vessel, reacting at a constant temperature of 150~200℃ for 8~15h, and naturally cooling to room temperature.

6. The method for preparing a multifunctional broadband electromagnetic absorbing composite material based on biomimetic periodic units and multi-level core-shell fillers as described in claim 2, characterized in that: The preparation of the high-loss coating includes the following steps: C1: Place the multi-stage core-shell filler, thermally conductive flexible polymer, diluent, and thixotropic agent into a mixer and stir at 1200~1700 rpm for 15~40 min to obtain mixture A; C2: Grind the mixture 2-5 times until the final viscosity of mixture A is 1×10⁻⁶. 5 cP ~ 1.5 × 10 5 cP; The preparation of the impedance matching coating includes the following steps: D1: Place the multi-stage core-shell packing material, spherical material, thermally conductive flexible polymer, diluent and thixotropic agent into a mixer and stir at 1200~1700 rpm for 15~40 min to obtain mixture B; D2: Grind the mixture 2-5 times until the final viscosity of mixture B is 7×10⁻⁶. 4 cP ~ 10×10 4 cP.

7. The method for preparing a multifunctional broadband electromagnetic absorbing composite material based on biomimetic periodic units and multi-level core-shell fillers as described in claim 6, characterized in that: The spherical material is glass microspheres with a particle size of 10~20μm, the thermally conductive flexible polymer includes thermally conductive silicone rubber or polyurethane, the diluent is xylene, and the thixotropic agent is fumed silica.

8. The method for preparing a multifunctional broadband electromagnetic wave absorbing composite material based on biomimetic periodic units and multi-level core-shell fillers as described in claim 2, characterized in that: In step A3, the biomimetic periodic unit (1) is impregnated, with high-loss coating as the innermost layer (101) and impedance matching coating as the outer layer (102), and impregnation is performed sequentially.

9. The method for preparing a multifunctional broadband electromagnetic absorbing composite material based on biomimetic periodic units and multi-level core-shell fillers as described in claim 8, characterized in that, The impregnation process of the electromagnetic absorbing composite material includes: E1: Preprocessing The biomimetic periodic unit (1) was rinsed with deionized water; After cleaning, the bionic cycle unit (1) is placed in a drying equipment for pre-drying; E2: Immersion Operation The pretreated biomimetic periodic unit (1) is placed in the immersion tank; The prepared high-loss coating is slowly added to the impregnation tank as the impregnation liquid. The amount of impregnation liquid added is based on immersing 2 / 3 of the biomimetic cycle unit (1). The biomimetic periodic unit (1) is immersed in the impregnation solution for 30~60 minutes; E3: Post-processing After soaking, the biomimetic periodic unit (1) was removed from the soaking tank and the excess soaking liquid on the surface was removed by draining. The drained biomimetic cycle unit (1) is placed in a drying device for drying; E4: After drying, the bionic periodic unit (1) is cooled to room temperature. Then, according to the parameters in step E3, the remaining 1 / 3 of the other side of the bionic periodic unit (1) is impregnated with impedance matching coating to obtain electromagnetic wave absorbing composite material.

10. The method for preparing a multifunctional broadband electromagnetic absorbing composite material based on biomimetic periodic units and multi-level core-shell fillers as described in claim 9, characterized in that, The impregnation process of the electromagnetic absorbing composite material includes: E1: Preprocessing The biomimetic periodic unit (1) was rinsed with deionized water for 5-10 minutes, and the rinsing pressure was controlled at 0.2-0.3 MPa. After cleaning, the bionic cycle unit (1) is placed in a drying equipment for pre-drying. The pre-drying temperature is 60~80℃ and the time is 1~2h. E2: Immersion Operation The pretreated biomimetic periodic unit (1) is placed in the immersion tank; The prepared high-loss coating is slowly added to the impregnation tank as the impregnation liquid. The amount of impregnation liquid added is based on immersing 2 / 3 of the biomimetic cycle unit (1). Start the vacuum equipment and evacuate the impregnation tank. The vacuum level is controlled between -0.085MPa and -0.095MPa, and the evacuation time is 15~30min. After vacuuming is completed, the vacuum equipment is turned off, and the biomimetic cycle unit (1) is kept immersed in the impregnation liquid for 30~60 minutes. During the immersion process, the impregnation liquid is stirred at a speed of 50~100 r / min to ensure that the concentration of the impregnation liquid is uniform. E3: Post-processing After soaking, the biomimetic cycle unit (1) is taken out of the soaking tank and the excess soaking liquid on the surface is removed by draining. The draining time is 5~10 minutes. The drained bionic cycle unit (1) is placed in a drying equipment for drying at a temperature of 80~120℃ for 2~4 hours. E4: After drying, the bionic periodic unit (1) is cooled to room temperature. Then, according to the parameters in step E3, the remaining 1 / 3 of the other side of the bionic periodic unit (1) is impregnated with impedance matching coating to obtain electromagnetic wave absorbing composite material.

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